1. Field of the Invention
The present invention relates generally to a method of and an apparatus for motion vector compensation, and more particularly, a method and an apparatus for motion vector compensation in receiving a high definition television signal based on a MUSE system.
2. Description of the Prior Art
NHK (Nippon Hoso Kyokai or Japan Broadcasting Corporation) has proposed a bandwidth compressed transmission system for transmitting a high definition television signal (high vision signal) on one channel. This bandwidth compressed transmission system is called MUSE (Multiple Sub-nyquist Sampling Encoding) system.
According to the standard of a high definition television, the number of scanning lines is 1125, a field frequency is 60 Hz, an interlace ratio is 2:1, a length-to-breadth ratio of a picture is 9:16, and a band of a video signal is wide, i.e., about 30 MHz. Therefore, in order to transmit the high definition television signal referred to as (HDTV signal hereinafter) without any modification, a bandwidth of two or more channels of DBS is required. The use of the MUSE system allows the bandwidth of a transmission signal to be compressed to 8 MHz, so that the HDTV signal can be transmitted on one channel of DBS.
FIG. 1 is a diagram showing a sampling pattern based on the MUSE system. In FIG. 1, a mark of a circle ( .circle. ), a mark of a square (.quadrature.), a mark of a solid circle ( ) and a mark of a solid square ( ) represent a sampling point in the 4n-th field, a sampling point in the (4n+1)-th field, a sampling point in the (4n+2)-th field and a sampling point in the (4n+3)-th field, respectively. T.sub.0 denotes a sampling interval, which corresponds to the reciprocal of a transmission sampling rate (16.2 MHz).
As described in, for example, NIKKEI ELECTRONICS issued by NIKKEI McGraw-Hill, Inc., Mar. 12, 1984, pp. 112-116, an article entitled "New Transmission System of High Definition Television", Monthly Report of NHK Science and Technical Research Laboratories, July, 1984, pp. 275-286, Terebi Gijyutu issued by Denshi Gijutsu Shuppan Kabushiki Kaisha, September, 1984, pp. 19-24, and Denpa Kagaku issued by NHK, April, 1984, pp. 103-108; an HDTV signal based on the MUSE system is formed in the following manner.
Sub-nyquist sampling in which a sampling phase is circulated every four fields is carried out for a luminance signal and a chrominance signal of a baseband. The chrominance signal is converted into two color difference signals (R-Y, B-Y), to be time-compressed to 1/4. A clock frequency of the luminance signal is 16.2 MHz, and a clock frequency of the color difference signal before time-compression is 4.05 MHz. Thus, a clock frequency of a time compressed color difference signal is 16.2 MHz. More specifically, a transmission sampling pattern of the HDTV signal is set to 16.2 MHz. The time compressed color difference signal is multiplexed in a line sequential manner in the horizontal blanking period of the luminance signal. More specifically, the two time compressed color difference signals R-Y and B-Y are alternately multiplexed every horizontal scanning period. In addition, in the vertical blanking period of the luminance signal, a control signal indicating, for example, data concerning a horizontal motion vector and a vertical motion vector and a sound/additional information signal are multiplexed. In the above described manner, in the HDTV signal based on the MUSE system is formed to be a TCI (Time Compressed Integration) signal based on a 2:1 interlace system. Meanwhile, vertical and horizontal synchronizing signals are multiplexed with same polarity as a video signal in the HDTV signal.
In a receiver for the HDTV signal, a picture is reproduced by combining data at sampling points in four fields. As shown in FIG. 2, the receiver for the HDTV signal comprises a frame memory 1 for interframe interpolation which is operated at a rate (32.4 MHz) of two times the transmission sampling rate. The frame memory 1 comprises a cascade circuit of two field memories 4 and 5 to interpolate a still region and a moving region of an image after interframe interpolation. Each of the field memories 4 and 5 has capacity of two fields, so that the frame memory 1 has capacity of four fields.
Data at a sampling point of an HDTV signal inputted to an input terminal is inputted to the frame memory 1 through a switch 3 which is switched at a clock rate 32 MHz of two times the transmission sampling rate. In addition, data at a sampling point approximately one frame before which is delayed by the frame memory 1 and then outputted is inputted to the frame memory 1 through the switch 3. Consequently, data of a luminance signal and a time compressed color difference signal in the present frame and data of a luminance signal and a time compressed color difference signal one frame before are combined with each other, to be inputted to the frame memory 1. The switch 3 is switched in synchronization with the received HDTV signal, so that the phase of the switching is inverted every frame and every line.
As shown in FIG. 3A, after the switch 3 is first switched to an input side 3a so that data ( .circle. mark) at a sampling point in the n-th field is inputted to an input terminal A of the frame memory 1, the switch 3 is switched on an output side 3b of the frame memory 1, so that data ( mark) at a sampling point one frame before which is 10 outputted from the frame memory 1 is inputted to the input terminal A of the frame memory 1. Similarly, data at a sampling point in the (n+1)-th field and data at a sampling point one frame before are alternately inputted to the frame memory 1 (not shown in FIG. 3A). Data thus combined is delayed by one frame (two fields) by the frame memory 1 and then, outputted from an output terminal B, to be combined with data ( mark) at a sampling point in the (n+2)-th field which is inputted to the input terminal 2. Therefore, data at a sampling point in the present frame which is inputted to the input terminal 2 is combined with data at a sampling point one frame before, so that interframe interpolation is carried out.
For example, in a field where data at a sampling point represented by " .circle. mark" shown in FIG. 1 is applied to the input terminal 2, the data at the sampling point represented by " .circle. mark " which is applied to the input terminal 2 and data at a sampling point one frame before which is outputted from the field memory 5 are alternately inputted to the field memory 4. Consequently, the data at the sampling point one frame before is inserted into the position of data represented by " mark" shown in FIG. 1. In addition, in a field where the data at the sampling point represented by " mark" shown in FIG. 1 is applied to the input terminal 2, the data at the sampling point represented by " mark" which is applied to the input terminal 2 and the data at the sampling point one frame before which is outputted from the field memory 5 are alternately inputted to the field memory 4. Consequently, the data at the sampling point one frame before is inserted into the position of the data represented by " .circle. mark" shown in FIG. 1. Similarly, in respective fields where data at a sampling point represented by ".quadrature. mark" and data at a sampling point represented by " mark" are applied to the input terminal 2, the data at the sampling point represented by ".quadrature. mark" and the data at the sampling point represented by " mark" which are applied to the input terminal 2 and data at respective sampling points one frame before which are outputted from the field memory 5 are alternately inputted to the field memory 4, respectively. Consequently, the data at the respective sampling points one frame before are inserted into the positions of the data represented by " mark" and ".quadrature. mark" shown in FIG. 1, respectively.
As described in the foregoing, data of two fields obtained by combining data at a sampling point in the present field with data at a sampling point one frame before are written to the field memory 4 every field as data in one field. The data of two fields written to the field memory 4 is delayed by one frame and then, read out from the field memory 5. Consequently, data at a sampling point which is lacking in each field is obtained by interframe interpolation. For example, if the data in the present field is data represented by " .circle. mark", data represented by " mark" is obtained by interframe interpolation.
The data thus combined is outputted to a circuit in the succeeding stage (not shown) as data of a luminance signal and a line compressed color difference signal in an image of one field.
Meanwhile, when the above described interframe interpolation is carried out for a motion picture portion, there occurs inconvenience such as multi-line blur. Therefore, in a receiver for an HDTV signal, interframe interpolation is generally carried out for only a still picture portion, while interfield interpolation by which a picture is formed using only data at a sampling point in the present field is carried out for a motion picture portion. If this intrafield interpolation is carried out, the quality of a reproduced image is slightly degrated, which does not present a large program because resolution of eyes relative to a fast moving picture is lowered, as compared with that relative to a still picture.
However, for example, the entire picture may be moved in the same direction by slow panning of a camera, to enter a motion picture state . The resolution of eyes is not so lowered relative to such movement. Therefore, when intrafield interpolation is carried out for such a motion picture, blur of an image is noticeable. In this case, if data at a sampling point one frame before which is combined with data at a sampling point in the present field can be shifted, interframe interpolation can be carried out, as for the still picture. On the side of transmission, horizontal and vertical motion vectors indicating the amount of movement of the entire picture are detected, so that data of the horizontal and vertical motion vectors are multiplexed on each field of the HDTV signal. In the receiver, the amount of delay in the frame memory is changed based on motion vectors in each field of the received HDTV signal, so that data at a sampling point
one frame before which is outputted from the frame memory is shifted by the amount of movement caused by panning, whereby motion vector compensation is carried out. Consequently, if and when the entire picture is moved in parallel in the same direction, interframe interpolation can be carried out, so that blur of an image can be prevented.
Meanwhile, data of the horizontal motion vector is set to 4 bits in units of a sampling interval T.sub.0 /2 shown in FIG. 1 such that compensation is carried out in a horizontal direction in the range of -8 to +7 clocks. In addition, data of the vertical motion vector is set to 3 bits in units of a horizontal scanning period H such that compensation is carried out in a vertical direction in the range of -4H to +3H.
The conventional horizontal motion vector compensation described in, for example, Japanese Patent Laying-Open Gazette No. 221090/1984 and the above described monthly report of NHK Science and Technical Research Laboratories is carried out in the following manner. 4-bit data of the horizontal motion vector is inputted to an input terminal 6 shown in FIG. 2. The amount of delay in the field memory 5 is changed every field in the range of -8 to +7 clocks based on the data of the horizontal motion vector, so that a position of data at a sampling point one frame before in the horizontal scanning period which is outputted from the frame memory 1 is shifted by the amount of movement caused by panning.
Meanwhile, the amount of delay in the field memory 5 is changed by controlling writing/reading to/from the field memories 4 and 5 or switching an output tap of a delay amount varying shift register (not shown) provided in the succeeding stage of the field memory 5.
According to the above described conventional method of horizontal motion vector compensation, a position of data at a sampling point one frame before is shifted in units of the sampling period T.sub.0 /2, so that good compensation in pixel units can be carried out for a luminance signal which is not time-compressed. However, considering a case in which the same compensation as that for the luminance signal is carried out for a time-compressed color difference signal, when the time compressed color difference signal is time-expanded to be returned to the original color difference signal, erroneous compensation is carried out by data which is shifted by a distance of four times a proper distance corresponding to the amount of movement of the picture, so that non-uniformity of color occurs.
Additionally, with respect to a chrominance signal, two types of color difference signals are transmitted in a line sequential manner, so that motion vector compensation can not be carried out in 1H units in a vertical direction.
Therefore, the conventional motion vector compensation is carried out only for the luminance signal. Thus, in the horizontal blanking period during which the time-compressed color difference signal is inputted, control of the amount of delay of the frame memory based on the horizontal and vertical motion vectors is stopped, so that motion vector compensation is not carried out for the time compressed color difference signal.
Thus, in the conventional receiver, if and when the entire picture is moved in parallel by panning or the like of a camera, interframe interpolation is carried out for only a luminance signal in a reproduced image while carrying out motion vector compensation, so that the same processing as that for a motion picture portion is performed for the chrominance signal using only data received every field. Therefore, imbalance of resolution occurs between the luminance signal and the chrominance signal, so that good color reproduction is not made.
However, as described above, the HDTV signal based on the MUSE system is an TCI signal, and the chrominance signal is time-compressed to 1/4 in the horizontal direction and multiplexed in a line sequential manner in the vertical direction, as compared with the luminance signal. Therefore, the same interpolation as that for the luminance signal can not be carried out for the chrominance signal using data of the motion vector produced based on the luminance signal on the side of transmission without any modification.
Japanese Patent Laying-Open Gazette No. 189893/1987 discloses a method of and an apparatus for carrying out motion vector compensation for a chrominance signal. According to this method, the chrominance signal is first time-expanded. Thus, interframe interpolation is carried out for two chrominance signals which come to have the same time axis as that of a luminance signal, based on data of a motion vector. In this case, processing performed when motion vector compensation corresponds to a shifting amount by even-numbered lines differs from processing performed when it corresponds to a shifting amount by odd-numbered lines.